I received the 1 mile as well and here are my "stats":
1. US Address
2. Three NW transactions this year from January through February 2009, including a Gift Registry bonus, Mountains of Miles reward, and a mileage transfer from DL to NW. My last flight credited to NW was 16 Nov 2008.
3. My DL and NW accounts are linked.
4. I transferred 230 miles from DL to NW (see above), but not the other way around.
5. I have 33 flight segments on DL this year and none credited to NW.